In some elevators, a linear electric motor is utilized for moving the elevator car between landing floors. Linear electric motors are especially useful for elevators having very long elevator shafts, that is, so called high-rise elevators. The problem with high-rise elevators is that the weight of the hoist rope becomes so high that the rope may not withstand its own weight, let alone the weight of the elevator car.
A typical electric linear motor is such that it has a long linear stator equipped with controllable electromagnetic components such as coils for generating magnetic field. The rotor, or “mover”, typically comprises permanent magnets, magnetic fields of which, when being in electromagnetic engagement with the “traveling” magnetic field of the stator, causes the rotor to move along the linear stator.
In some earlier attempts, the linear electric motors have been advantageously utilized in elevators as described hereinabove. In some solutions, the windings have been arranged to the linear stator which, especially in high-rise elevators, requires considerable amount of windings to be winded since the length of the linear stator can be from 50 meters up to hundreds of meters, for instance.
In an earlier attempted solution, an electric linear motor having permanent magnets and controllable electromagnetic components, such as windings, arranged to the mover which is mounted to the elevator car. The linear stator, in contrary, comprises ferromagnetic material and is shaped to have stator teeth. Thus, the teeth arranged sequentially to the linear stator form magnetic poles when being in electromagnetic engagement with the mover generating magnetic field via controllable windings and permanent magnets. This arrangement is advantageous because the windings are arranged to the mover or movers instead of long linear stator or stators, thus saving winding material.
A challenge with the earlier attempts is that although the mover, and thus the elevator car alongside with the mover, can be moved along the linear stator by known methods utilizing varying magnetic field generated by motor the motor current, the elevator typically needs additional windings for levitating the mover, that is, to maintain an air gap or air gaps between the mover and the stator. Another challenge is that the mover tends to tilt with respect to the linear stator, that is, to turn in clockwise or counter-clockwise direction. The tilting may be felt by passengers inside the elevator car as uncomfortable vibrations.
There is thus still a need to provide a simple electric linear motor capable of controlling the levitation and the tilting of the mover of the electrical linear motor.